First, a quick history. Kodak Preps 5.x series (including 5.1, 5.2, and 5.3) was released during a transitional era in prepress. Many printers found version 5.3.3 to be the "sweet spot" for several reasons:
The safest way to obtain the Preps 5.3.3 installer is through official Kodak portals. kodak preps 533 download link